1. Technical Field
The present invention relates to wireless communications and, more particularly, wideband wireless communication systems.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards, including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of a plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via a public switch telephone network (PSTN), via the Internet, and/or via some other wide area network.
Each wireless communication device includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage (de-modulator). The low noise amplifier receives an inbound RF signal via the antenna and amplifies it. The one or more intermediate frequency stages mix the amplified RF signal with one or more local oscillations to convert the amplified RF signal into a baseband signal or an intermediate frequency (IF) signal. As used herein, the term “low IF” refers to both baseband and intermediate frequency signals. A filtering stage filters the low IF signals to attenuate unwanted out of band signals to produce a filtered signal. The data recovery stage recovers raw data from the filtered signal in accordance with the particular wireless communication standard. Alternate designs being pursued at this time further include direct conversion radios that produce a direct frequency conversion often in a plurality of mixing steps or stages.
The various above described technologies are being utilized in a wide range of applications including the aforementioned wireless local area networks that are formed according to I.E.E.E. 802.11(a), 802.11(b), 802.11(g) and Bluetooth standards among others. As these standards evolve, however, there are multiple design pressures that sometimes are in conflict. For example, there is always demand for increasing levels of speed, reliability and more generally, data throughput. Continuous bit rate data, for example, streaming data, push the envelope of technical ability and performance.
As technologies evolve, there further is a need to maintain compatibility between newer and older technologies. Such compatibility is problematic, however, when a change in fundamental physical layer technology is made to satisfy the demand for increased speed and throughput. One example of this type of migration from one type of physical layer (layer 1) technology is seen in Bluetooth. The Bluetooth standards originally called for data rates of 1 million bits per second (Mbps) utilizing frequency shift keying modulation techniques. Newer releases of the Bluetooth standard, however, call for data transmission rates of 2 and 3 Mbps utilizing phase shift keying modulation techniques. Thus, while the fundamental modulation techniques are different, there is also a Bluetooth requirement for radio transceivers to maintain backwards compatibility. At the same time, there also exist spectral mask requirements that cannot be violated even for the instant of switching from one modulation type to another. It is known, however, that abruptly changing from one modulation type to another can result in spectral mask violations. Thus, the need for the invention arises from the requirement that during the transition between the two modulation formats, the transmitted RF spectrum comply with strict spectral mask limitations set by the applicable regulatory bodies. Typically, such requirements cannot be met when modulation switching occurs with abrupt, discontinuous waveforms. A need exists, therefore, for a radio transmitter that can transition from one modulation technique to another in a continuous, smooth manner that does not violate spectral mask requirements.